Apparatus, a system and a method relating to hemodialysis, hemodiafiltration, hemofiltration or peritoneal dialysis

ABSTRACT

The invention relates to an apparatus for hemodialysis, hemodiafiltration, hemofiltration or peritoneal dialysis. The apparatus comprises at least one conduit ( 10, 14 ) in which a dialysis and/or infusion fluid is intended to flow. The apparatus has a measurement unit ( 48 ) for measuring at least one optically active substance in the fluid. The measurement unit ( 48 ) is arranged to measure the concentration of the substance in said fluid by measuring the influence said substance in the fluid has on a polarized beam of light which is transmitted through said fluid. The invention also concerns a system including such an apparatus as well as a method of carrying out a measurement of the concentration of an optically active substance in a dialysis and/or infusion fluid.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus for hemodialysis,hemodiafiltration, hemofiltration or peritoneal dialysis. The apparatuscomprises at least one conduit in which a dialysis and/or infusion fluidis intended to flow. The apparatus comprises a measurement unit formeasuring at least one substance in said fluid.

The invention also concerns a system including such an apparatus as wellas a method concerning hemodialysis, hemodiafiltration, hemofiltrationor peritoneal dialysis.

Hemodialysis is a treatment designed to correct the chemical compositionof blood by removing accumulated metabolic products and adding buffer ina process of diffusion through a natural or synthetic semi-permeablemembrane.

A conventional kind of hemodialysis apparatus is well known to a personskilled in the art. An example of such an apparatus is described inconnection with FIG. 1 in EP-A2-904 789. A hemodialysis apparatus isused to treat a patient suffering from kidney failure. In a dialysisapparatus a dialysis fluid (dialysis solution) is prepared. The dialysisfluid is used to achieve dialysis in a dialyser that is part of thehemodialysis apparatus. The dialysis fluid can be prepared in theapparatus by feeding water and one or more concentrates to theapparatus. The apparatus may also be arranged to provide the patientwith an infusion solution. Such an infusion solution may be the same ordifferent than the dialysis fluid. Since a hemodialysis apparatus iswell known to a person skilled in the art, it will not be described inall its details here.

Hemofiltration is a treatment designed to remove accumulated metabolicproducts from blood by the process of convective transport as aconsequence of ultrafiltration through a semi-permeable membrane ofhigh-flux type; the volume of filtered fluid exceeding the desiredweight loss is replaced by sterile pyrogen-free infusion solution. In apure hemofiltration process, normally no dialysis fluid is used.

Hemodiafiltration is a treatment designed to remove accumulatedmetabolic products from blood by a combination of diffusive andconvective transport through a semi-permeable membrane of high-fluxtype; fluid is removed by ultrafiltration and the volume of filteredfluid exceeding the desired weight loss is replaced by sterile,pyrogen-free infusion solution.

There exist apparatuses that can be used for both hemodialysis andhemofiltration, as well as for hemodiafiltration.

There also exist apparatuses for peritoneal dialysis. In peritonealdialysis no dialyser that is part of an apparatus is needed. Instead theperitoneum of the patient is used as a dialysis membrane. Also in anapparatus for peritoneal dialysis, a dialysis fluid and/or an infusionfluid is added.

It should also be mentioned that it is known to provide apparatuses ofthe above described kinds with a measurement unit for measuring somesubstance in the dialysis or infusion fluid. The apparatus may forexample be provided with a measurement unit that measures theconductivity of the dialysis fluid in order to estimate theconcentration of the dialysis concentrate that is mixed with water inthe apparatus.

Often a concentrate including glucose or a similar substance, is addedto apparatuses of the above mentioned kinds. The glucose is oftenprovided as a concentrate that is fed to the apparatus. The glucoseconcentrate can be provided in different kinds of containers from whichthe concentrate is fed to the apparatus. Since such concentrates may beprovided with different glucose concentrations, it is important toensure that a concentrate of the correct glucose concentration is fed tothe apparatus. Sometimes, the concentrate including glucose is providedin a flexible fluid bag. Such a bag may comprise a plurality ofcompartments. The compartments are to be connected to each other suchthat the fluids of the different compartments mix with each other beforethe fluid is fed to the apparatus. In such a fluid bag, the glucoseconcentrate may be included in one compartment. In this kind of fluidbag, it is important to ensure that the contents of the differentcompartments have been mixed with each other before the fluid is fed tothe apparatus. Due to the human factor, it is possible to make mistakes,such that a container with the wrong concentration of glucose isconnected to the apparatus in question, or such that a flexible fluidbag with different compartments is connected to an apparatus without thecontents of the different compartments having been properly mixed witheach other before the fluid is fed to the apparatus.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an apparatus of thekind that is defined in the first paragraph above and which makes itpossible to measure the concentration of a substance in a fluid that isfed to the apparatus or that is transported in the apparatus. A furtherobject is to provide an apparatus with means which makes it possible toavoid the above mentioned possible mistakes concerning the concentrationof a substance added to the apparatus. This substance can be glucose ora similar substance. A further object is to provide such means that arecomparatively simple and inexpensive to implement in an apparatus of theabove kind. A further object is to provide such an apparatus which in areliable manner detects whether the concentration of such a substance inthe fluid is correct.

The above objects are achieved by an apparatus of the kind that isdefined in the first paragraph above and that is characterised in thatthe substance that is to be measured is an optically active substance,wherein the measurement unit is arranged to measure the concentration ofsaid substance in said fluid by measuring the influence said substancein the fluid has on a polarised beam of light which is transmittedthrough said fluid.

The inventor of the present invention has thus realised that since asubstance such as glucose is an optically active substance, an apparatusof the above mentioned kind can be provided with a measurement unit thatmeasures the influence that the substance in the fluid has on apolarised beam of light. With such a measurement unit, it can be ensuredthat a substance of the correct concentration is fed into or through theapparatus. Such a measurement unit can also be constructed quite simplyand does not have to be expensive.

In this context it can be mentioned that it is known that for exampleglucose is an optically active substance. It is also known that theconcentration of optically active substances can be measured bytransmitting a polarised beam of light through the substance. Forexample U.S. Pat. No. 5,357,960 describes a method and an apparatus forquantitative determination of an optically active substance in vivo. WO01/84121 A1 describes a method and a device for polarimetric measurementof the concentration of for example glucose in blood in vivo. Theapparatuses and the methods disclosed in these documents are quitecomplicated, since the concentration of the substances to be measured invivo is quite low. The inventor of the present invention has howeverrealised that the concentrations to be measured in an apparatusaccording to the present invention, usually are very high. The inventorhas therefore realised that a measurement unit arranged in an apparatusaccording to the present invention can be made quite simple and stillgive a very accurate measurement of the concentration of the substancein question.

It should be mentioned that the concepts dialysis fluid and infusionfluid in this document are not only meant to refer to the final dialysisor infusion fluid but also to a concentrate which is mixed with otherconcentrates and/or diluted in order to obtain the final dialysis orinfusion fluid.

It should also be noted that when in this document “light” is mentioned,this concept is meant to cover not only electromagnetic radiation in thevisible wavelength range but also electromagnetic radiation of otherwavelengths.

According to a preferred embodiment, the apparatus includes a pluralityof inlets for different matters, wherein the apparatus is arranged suchthat the different matters introduced via said inlets will be mixed witheach other in said apparatus, wherein the measurement unit is positionedin or at said apparatus such that the concentration of said substance insaid fluid is measured before the fluid has obtained its final form inthe apparatus by being mixed with all the other matters introduced viasaid inlets. Before the fluid has been mixed with all the other matters,the fluid contains normally a higher concentration of the substance tobe measured. Therefore, the invention is particularly useful to measurethe concentration of the substance before the fluid has obtained itsfinal form in the apparatus.

Preferably,.said plurality of inlets include a first inlet via which thefluid to be measured is to be introduced into the apparatus, wherein themeasurement unit is positioned in or at the apparatus such that theconcentration of said substance in said fluid is measured before saidfluid, that is introduced via said first inlet, has been mixed in theapparatus with any other matter introduced via the other of saidplurality of inlets. According to this embodiment, the concentration ofthe substance is thus measured before the fluid has been mixed with anyother substance in the apparatus. The concentration of the substance inthe fluid is therefore particularly high. Furthermore, if theconcentration of the substance is found to be wrong, it is possible tostop the feeding of the fluid to the apparatus at an early stage.

According to a further embodiment, the measurement unit is designed tomeasure a concentration of said substance that is above 100 g/l. Themeasurement unit can particularly be designed to measure theconcentration of a sugar in said fluid, preferably in the form ofglucose. When the concentration of the substance is above 100 g/l it isparticularly advantageous to use the present invention, since themeasurement unit can be designed in a quite simple manner. Since theconcentration of for example glucose that is fed from a concentrate toan apparatus is normally essentially higher than 100 g/l, the apparatusaccording to the present invention is particularly useful.

According to a further embodiment, the apparatus includes means arrangedto generate a warning signal if the measured concentration of saidsubstance in said fluid does not fulfil a predetermined requirement. Thewarning signal may for example be an electrical signal which indicatesthat a certain measure is to be carried out. For example, the signal maycause the dialysis process to stop and/or may cause a light or soundsignal to be emitted as a warning to the operator of the apparatus.

According to a preferred embodiment, the apparatus includes an at leastpartly transparent conduit in said apparatus or at an inlet to saidapparatus, through which transparent conduit the fluid to be measured isto pass, wherein said measurement unit is positioned and arranged toproduce a polarised beam of light that is passed through the fluid to bemeasured at said at least partly transparent conduit. By passing thefluid through a transparent conduit, it is possible to pass a beam oflight through the transparent conduit and thereby through the fluid.

The measurement unit is with advantage arranged to provide aplane-polarised beam of light. The measurement unit can thereby bearranged with measurement means that measure an entity that indicateswith which angle the plane of polarisation of said polarised beam oflight has rotated when said polarised beam of light has passed throughthe fluid. The measurement means can thereby comprise a light intensitydetector. By measuring with which angle the polarised beam of light hasbeen rotated in the fluid, a measure of the concentration of theoptically active substance in the fluid is obtained.

The invention also relates to a system comprising an apparatus accordingto any of above embodiments and a container including a fluid, whereinthe container is connected to the apparatus such that the fluid in thecontainer is fed to the apparatus, and wherein said measurement unit isarranged to measure the concentration of said substance in the fluidfrom the container. With such a system, it is thus possible to measurewhether the correct concentration of the substance in the fluid from thecontainer is fed to the apparatus.

The container is preferably of the kind that includes at least twocompartments, and wherein the contents of these compartments are to bemixed before the fluid leaves the container. The container can be aflexible fluid bag, in which the concentration of said substance to bemeasured is at least 100 g/l. As has been mentioned above, it isimportant to be able to measure whether the contents of the differentcompartments in such a container have been mixed correctly before thefluid is fed to the apparatus. This can be done in an efficient andaccurate but still inexpensive manner with an apparatus or a systemaccording to the invention.

The invention also relates to a method of carrying out a measurement ofthe concentration of an optically active substance in a dialysis and/orinfusion fluid, which fluid is arranged to be fed to and/or through anapparatus for hemodialysis, hemodiafiltration, hemofiltration orperitoneal dialysis. The method comprises the steps of: providing apolarised beam of light; transmitting said polarised beam of lightthrough said fluid; and detecting the influence that said substance inthe fluid has on the polarised-beam of light which is passed through thefluid such that an indication of the concentration of said substance inthe fluid is obtained. With such a method, advantages corresponding tothose described above in connection with the apparatus and with thesystem are obtained.

The substance is preferably a sugar, such as glucose. The fluid can be aconcentrate that is to be mixed with other substances and/or diluted insaid apparatus. The fluid is preferably fed to said apparatus from acontainer, for example a flexible fluid bag, which can include at leasttwo compartments, and wherein the contents of these compartments aremixed before the fluid leaves the container.

Further preferred manners of carrying out the method are described inthe claims below and in the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a dialysis apparatus and a system accordingto the present invention.

FIG. 2 shows schematically a measurement unit that can be used in theapparatus and in the system according to the invention.

FIG. 3 shows schematically an alternative embodiment of the measurementunit.

FIG. 4 shows a schematic flow chart of an embodiment of the methodaccording to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows schematically an apparatus according to the invention. Theapparatus has a first flow circuit 10 for a dialysis solution and asecond flow circuit 12 for blood. The apparatus according to thisembodiment also has a conduit 14 for infusion solution. A drip chamber16 is arranged as part of the second flow circuit 12. Also the conduit14 leads to the drip chamber 16. The connections 18 and 20 are to beconnected to a patient. A dialyser or hemofilter 21 is connected to thefirst flow circuit 10 and to the second flow circuit 12. The dialyser orhemofilter 21 is provided with a semi-permeable membrane 22. It shouldbe mentioned that an apparatus for peritoneal dialysis does of coursenot have any dialyser 21, since in this case the peritoneum of thepatient functions as a dialyser membrane.

A by-pass conduit 25 is arranged between valves 23 and 24. The valves 23and 24 can thus be set such that the dialysis solution passes throughthe by-pass conduit 25 instead of through the dialyser 21.

In the shown embodiment, the apparatus has inlets 26, 28, 30 and 32. Thenumber of inlets may of course vary from apparatus to apparatus. Theinlet 26 is an inlet for pure water. The inlets 28, 30 and 32 constituteinlets for different concentrates which together with the water are toform the dialysis solution. The correct composition of the dialysissolution is prepared in a preparatory unit 34. An outlet for thedialysate is indicated by 36. 38 indicates a processor unit or acomputer that controls the operation of the apparatus.

Since a dialysis apparatus is well known to a person skilled in the art,there is no need to show all the details of such an apparatus here.Neither is there any need to explain the function of such an apparatusin detail. The apparatus of course has many more parts, such as pumps,flow metres etc.

The apparatus described so far has a conventional construction known toa person skilled in the art.

The different concentrates needed for the dialyses solution may be fedto the apparatus from different containers. It is for example known thatat least some concentrate can be fed from a container in the form of afluid bag that contains two or more compartments. FIG. 1 showsschematically such a fluid bag 39 that is connected to the inlet 32. Thefluid bag 39 is normally suspended at a level above the inlet 32 and isconnected to the inlet 32 via a tube 40. In the shown example, the fluidbag 39 comprises two compartments 42 and 44. One compartment, forexample the compartment 42, may include a glucose solution. Before thecontent of the bag 39 is fed to the inlet 32, the contents of the twocompartments 42 and 44 are to be mixed with each other. This is done byopening a connection in a sealing 46 between the two compartments 42,44. It is important that the sealing 46 is actually broken such that thecontents of the two compartments 42 and 44 are mixed before theconcentrate is fed to the inlet 32, because if this is not the case,then the correct concentrate would not be fed to the inlet 32. Theconcentration of the glucose in the compartment 42 may for example be570 g/l. When the contents of the two compartments 42 and 44 have beenmixed, the concentration of glucose in the concentrate that is fed tothe inlet 32 should for example be 400 g/l.

In order to measure that actually the correct concentration of glucoseis fed to the apparatus, the apparatus according to the presentinvention is provided-with a measurement unit 48. The measurement unit48 is in this case arranged at the inlet 32. It should be noted that itis within the scope of the invention that the measurement 48 is arrangedat other parts of the apparatus. For example, the measurement unit 48,or an additional measurement unit, could be positioned in the first flowcircuit 10 or in the conduit 14. However, it is advantageous to arrangethe measurement unit 48 at the inlet 32 for at least two reasons.Firstly, the concentration of the glucose is much higher at the inlet 32than in other parts of, the apparatus. The measurement unit 48 doestherefore not have to be so sensitive when it is positioned at the inlet32. The measurement unit 48 can therefore be designed in a quite simpleand inexpensive manner. Secondly, it is advantageous to position themeasurement unit 48 at the inlet 32, since if the wrong concentration ofglucose would be detected by the measurement unit 48, then the feedingof the concentrate from the fluid bag 39 can be stopped at an earlystage.

With reference to FIG. 2, the measurement unit 48 will be described insome more detail. The measurement unit 48 is arranged to measure anoptically active substance. According to this example, the opticallyactive substance is glucose. The measurement unit 48 is arranged tomeasure the concentration of the optically active substance, i.e. inthis case glucose, by measuring the influence that the:substance in thefluid has on a polarised beam of light that is transmitted through -thefluid.

The theory of optical activity and how to measure with a polarised beamof light will not be described in all its details here, since thistheory is known to a person skilled in the art and since the theory isdescribed in different text books, such as Optics by Hecht and Zajec,Addison-Wesley Publishing Comp. 1974, see in particular pages 255-260.Basically, the measurement can be carried out by transmitting aplane-polarised beam of light through the fluid in question. The planeof polarisation will thereby be rotated when the beam of light passesthrough the fluid. The angle with which the plane of polarisation isrotated depends on the concentration of the optically active substancein the fluid as well on the distance through the fluid that the beam oflight has passed. If the angle of rotation is measured, and if thedistance through the fluid is known, the concentration of the opticallyactive substance in the fluid may be calculated.

FIG. 2 thus schematically shows an embodiment of the measurement unit 48that forms part of the apparatus according to the invention. Themeasurement unit 48 includes a sample cell 50. The fluid to be measuredis included in the sample cell 50. The sample cell 50 can be positionedsuch that all the fluid that is to be measured passes through the samplecell 50. The inlet 51 to the sample cell 50 can be connected to the tube40 from the container 39 (see FIG. 1). The fluid exits the sample cell50 via an outlet 32. This outlet 32 can thus be an inlet to thepreparatory unit 34 shown in FIG. 1. According to this embodiment, themeasurement unit 48 is thus positioned in the apparatus such that theconcentration of the glucose is measured before the fluid from the fluidbag 39 is mixed with any other substance that will be included in thedialysis, solution. The sample cell 50 has a first transparent window 54and a second transparent window 56. The sample cell 50 is thus designedsuch that a beam of light can pass through the sample cell 50 andthereby through the fluid that is located in the sample cell 50. Thefirst 54 and second 56 windows are preferably made of a material withoutinternal birefringence, in order to avoid that these windows-54, 56 willhave an influence on the measurement result.

The measurement unit also comprises a light source 58 that produces abeam of light that is passed through the sample cell 50. The lightsource 58 should preferably be monochromatic or near monochromatic. Aninexpensive light emitting diode (LED) can be used as the light source58. The light source 58 should produce a sufficiently collimated beam oflight. If necessary, a collimating lens 60 may be positioned in the beampath from the light source 58. The beam of light passes through a beamsplitter 62 that preferably reflects only a small portion of the lightbeam, while the major part of the light beam passes through the beamsplitter 62. The beam that passes through the beam splitter 62 alsopasses through a first polariser 61 that produces a plane-polarised beamof light. It should be mentioned that the beam splitter 62 does notnecessarily have to be positioned between the light source 58 and thepolariser 61. The beam splitter 62 could also be positioned between thepolariser 61 and the sample cell 50. In FIG. 2 it is indicated by arrowsthat the beam of light is polarised in the plane of the figure. Whenthis plane-polarised beam of light passes through the sample cell 50,the plane of polarisation will be rotated depending on the distancebetween the first 54 and second 56 windows and depending on theconcentration of an optically active substance in the sample cell 50.

After having passed through the sample cell 50, the beam of light passesthrough a second polariser 63. The second polariser 63 can for examplebe arranged such that the polarisation direction of the second polariser63 is perpendicular to that of the first polariser 61. In FIG. 2 this isindicated by the symbol next to the polariser 63. According to anotherpossible embodiment, the second polariser 63 (or the second polariser 63together with the photo detector 64) can be arranged to be rotatablearound the optical axis. In this case the angle with which the plane ofpolarisation of the polarised beam of light has rotated when the beamhas passed through the fluid can be measured by rotating the secondpolariser 63 until a maximum (or, alternatively, a minimum) lightintensity is detected by the photo detector 64. The rotational angle ofthe polariser 63 then indicates with which angle the plane ofpolarisation has been rotated.

The beam that has passed through the second polariser 63 impinges on afirst photo detector 64. The photo detector 64 thus measures theintensity of light impinging thereon. If there is no optically activesubstance in the sample cell 50, the plane of polarisation of the lightbeam will not change when passing through the sample cell 50. If thesecond polariser 63 is arranged as in FIG. 2, the photo detector 64 willthus detect a minimum intensity of light. On the other hand, if there isan optically active substance of such a concentration in the sample cell50 that the plane of polarisation is rotated 90° while passing throughthe sample cell 50, the photo detector 64 will detect a maximumintensity of light. When the optically active substance in the samplecell 50 is of such a concentration that the plane of polarisation willrotate between 0° and 90° , the photo detector 64 will detect anintensity of light that depends on the degree of rotation of the planeof polarisation. The detected light intensity at the photo detector 64is proportional to sin²θ where θ is the angle of rotation of the planeof polarisation. By detecting the light intensity at the first photodetector 64, an indication of the concentration of the optically activesubstance in the fluid in the sample cell 50 is thus obtained. Thelength of the sample cell 50, i.e. a distance between the first 54 andsecond 56 windows, should be chosen such that a suitable rotation ofplane of polarisation is obtained for the concentrations which arenormally measured by the measurement unit 48. It has been found that alength of the sample cell 50 of between 5 mm and 60 mm, preferablybetween 10 mm and 40 mm is suitable for this application, when theconcentration of the glucose to be measured is above 100 g/l, preferablyabove 300 g/l.

In the shown embodiment, the measurement unit 48 also comprises a secondphoto detector 66 that detects the beam reflected by the beam splitter62. The second photo detector 66 is used to detect variation in thelight intensity from the light source. Thereby the measurement detectedby the first photo detector 64 can be compensated for such variation.The first and second photo detectors are preferably connected to aprocessor unit, for example to the processor unit 38 described inconnection with FIG. 1. The concentration of the optically activesubstance in the fluid can be measured continuously while the fluidflows through the sample cell 50. However, it is also possible tomeasure this concentration intermittently and also when there is no flowthrough the sample cell 50.

Since the first 64 and second 66 photo detectors are connected to theprocessor unit 38, the processor unit 38 can be arranged to generate awarning signal if the measured concentration of the substance is outsidea pre-set requirement. The warning signal may for example cause thedialysis process to stop, for example by setting the valves 23 and 24such that the dialysis fluid passes through the by-pass conduit 25. Asignal, such that a sound or light signal, can also be produced in orderto warn the person operating the apparatus that the concentration in thefluid is not correct.

Another embodiment of the measurement unit 48 is schematically shown inFIG. 3. The same reference numbers are used for the correspondingcomponents as in FIG. 2. According to this embodiment, there is no beamsplitter 62 before the sample cell 50. The second polariser 63 in FIG. 2has been substituted by a polarising beam splitter 68. The polarisingbeam splitter 68 can be designed such that light polarised in the planeof the figure is transmitted through the beam splitter 68 while lightpolarised perpendicular thereto is reflected by the beam splitter 68towards the second photo detector 66. The ratio between the intensitydetected by the photo detector 64 and the photo detector 66 thus dependson the rotation of the plane of polarisation, and thereby on theconcentration of the optically active substance in the sample cell 50.The embodiment of FIG. 3 has the advantage that since the ratio betweenthe intensity detected by the photo detector 64 and the photo detector66 is analysed, a variation in the intensity of the light emitted fromthe light source 58 does not influence the detection. Furthermore, theopacity of the fluid in the sample cell 50 does not influence the resultof the measurement. It should be noted that FIG. 2 and FIG. 3schematically show two possible embodiments of the measurement unit 48.Modifications of or alternatives to these embodiments are evident to aperson skilled in the art without departing from the scope of thepresent invention.

A system according to the invention comprises an apparatus as describedabove together with a container 39 including the fluid to be analysed;for example a container in the form of a fluid bag 39. FIG. 1 thus alsoillustrates an embodiment of a system according to the invention. Asexplained above, the fluid bag 39 may comprise a plurality ofcompartments 42, 44. The concentration of the substance, such asglucose, that is fed from the fluid bag 39 to the apparatus ispreferably at least 100 g/l, more preferred at least 300 g/l. Ameasurement unit 48 that is included in the invention is particularlyuseful for measuring such relatively high concentrations, since themeasurement unit can be constructed in a simple and inexpensive manner.

FIG. 4 schematically shows a flow chart of a method according to theinvention for carrying out a measurement of the concentration of anoptically active substance in a dialysis and/or infusion fluid, whichfluid is arranged to be fed to and/or through an apparatus forhemodialysis, hemodiafiltration, hemofiltration or peritoneal dialysis.According to this example of how to carrying out the method, the methodcomprises the following steps.

A container 39 is provided. The container 39 is a flexible fluid bag 39with at least two compartments 42, 44.The contents of the twocompartments 42, 44 are to be mixed before the fluid leaves thecontainer 39. The concentration of the substance in the fluid at theposition where the measurement is carried out is to be at least 100 g/l.The fluid is fed from the container 39 to the apparatus. The fluidpasses through an at least partly transparent conduit 50, preferably atan inlet 32 to the apparatus. A plane-polarised beam of light isproduced. The plane-polarised beam of light is transmitted through thefluid. An entity is measured that indicates with which angle the planeof polarisation of the polarised beam of light has been rotated whenpassing through the fluid. An indication of the concentration of thesubstance is thus obtained.

The invention is not limited to the described embodiments but may bevaried and modified within the scope of the following claims.

1. An apparatus for hemodialysis, hemodiafiltration, hemofiltration orperitoneal dialysis, comprising at least one conduit in which a dialysisand/or infusion fluid is intended to flow, comprising a measurement unitfor measuring at least one substance in said fluid, said substance beingoptically active, wherein the measurement unit is arranged to measurethe concentration of said substance in said fluid by measuring theinfluence of said substance on a polarized beam of light transmittedthrough said fluid.
 2. An apparatus according to claim 1, furthercomprising a plurality of inlets for different matters, said differentmatters being mixed with each other after being introduced via saidinlets, wherein the measurement unit is configured to measure theconcentration of said substance in said fluid before the fluid is mixedwith the other different matters introduced via said inlets.
 3. Anapparatus according to claim 2, wherein said plurality of inlets includea first inlet for introducing the fluid to be measured into theapparatus, said measurement unit being configured to measure theconcentration of said substance in said fluid before said fluid, that isintroduced via said first inlet, is mixed in the apparatus with anyother different matters introduced via another of said plurality ofinlets.
 4. An apparatus according to claim 1, wherein said measurementunit is designed to measure a concentration of said substance above 100g/l.
 5. An apparatus according to claim 1, wherein said measurement unitis designed to measure the concentration of a sugar in said fluid.
 6. Anapparatus according to claim 5, wherein said sugar is glucose.
 7. Anapparatus according claim 1, further comprising means arranged togenerate a warning signal if the measured concentration of saidsubstance in said fluid does not fulfill a predetermined requirement. 8.An apparatus according to claim 1, further comprising an at least partlytransparent conduit in said apparatus or at an inlet to said apparatus,said transparent conduit being configured to carry the fluid to bemeasured, wherein said measurement unit is configured to produce apolarized beam of light that is passed through the fluid to be measuredat said at least partly transparent conduit.
 9. An apparatus accordingto claim 1, wherein said measurement unit is arranged to provide aplane-polarized beam of light.
 10. An apparatus according to claim 9,wherein said measurement unit further comprises a measurement device tomeasure an entity, said entity indicating the angle at which the planeof polarization of said polarized beam of light has rotated when saidpolarized beam of light has passed through the fluid.
 11. An apparatusaccording to claim 10, wherein said measurement device comprises a lightintensity detector.
 12. A system comprising an apparatus according toany claim 1, further comprising a container housing a fluid, wherein thecontainer is connected to the apparatus to allow the fluid housed in thecontainer he to be fed to the apparatus, and said measurement unit isarranged to measure the concentration of said substance in the fluid fedfrom the container.
 13. A system according to claim 12, wherein thecontainer includes at least first and second compartments havingcontents, the contents of the first and second compartments being mixedbefore the fluid leaves the container.
 14. A system according to claim12, wherein said container is a flexible fluid bag.
 15. A systemaccording to claim 12, wherein the concentration of said substance insaid container is at least 100 g/l.
 16. A method for carrying out ameasurement of the concentration of an optically active substance in adialysis and/or infusion fluid, comprising the steps of: feeding a fluidto and/or through an apparatus for hemodialysis, hemodiafiltration,hemofiltration or Peritoneal dialysis; providing a polarized beam oflight; transmitting said polarized beam of light through said fluid; anddetecting the influence of said substance on the polarized beam of lightwhich is passed through the fluid to measure the concentration of saidsubstance in the fluid.
 17. A method according to claim 16, wherein saidsubstance is a sugar.
 18. A method according to claim 17, wherein saidsugar is glucose.
 19. A method according to claim 16, wherein said fluidis a concentrate that is to be mixed with other substances and/ordiluted in said apparatus, said concentration measurement on said fluidbeing made before the fluid is mixed with other substances and/ordiluted in said apparatus.
 20. A method according to claim 16, whereinsaid fluid is fed to said apparatus from a container.
 21. A methodaccording to claim 20, wherein said container includes at least firstand second compartments having contents, the contents of the first andsecond compartments being mixed before the fluid leaves the containers.22. A method according to claim 20 or 21, wherein said container is aflexible fluid bag.
 23. A method according to claim 16, wherein theconcentration of said substance in said fluid at the position where themeasurement is carried out is at least 100 g/l.
 24. A method accordingto claim 16, further comprising the step of generating a warning signalif the measured concentration of said substance in said fluid does notfulfill a predetermined requirement.
 25. A method according to claim 16,wherein said feeding step further comprises the sub-step of: feedingsaid fluid through an at least partly transparent conduit in saidapparatus or at an inlet to said apparatus, wherein said polarized beamof light is transmitted through said fluid at said at least partlytransparent conduit.
 26. A method according to claim 16, wherein saidpolarized beam of light is a plane-polarized beam of light.
 27. A methodaccording to claim 26, wherein the step of detecting the influence ofsaid substance on the polarized beam of light further comprisesmeasuring an entity indicating the angle the plane of polarization ofsaid polarized beam of light has rotated when said polarized beam oflight has passed through the fluid.